1. Field of the Invention
The present invention relates to a method and apparatus for delivering flat articles, in particular but not exclusively printed sheet signatures hereinafter referred to as xe2x80x9csignaturesxe2x80x9d.
2. Brief Description of the Prior Art
Traditionally, loading of bindery line systems, generally comprising a hopper and a rotary feeding drum, is manually accomplished by an attendant. When the signatures are coming from a folding operation, they are tightly compressed to form a bundle and some of them frequently adhere to each other depending on various printing and storage conditions. It is well known in the art that the reliability and through-output of the bindery line is mainly lying on the ability to properly operate signature separation, as traditionally executed by the attendant, so that the feeding system will continuously succeed at transferring one signature at a time to the gathering conveyer, thus avoiding costly interruptions of the bindery line. The manual operation of separation is usually carried-out by the attendant by taking a pile of signatures and bending the pile back and forth a few times. Additionally, some tapping of the edges of the pile on a generally horizontal flat surface may be performed. More recently, automatic hopper loaders have been provided by the industry to accomplish the task of loading feeding systems, but the main challenge still resides in performing proper separation of the signatures prior to feeding.
While in some situations currently available loaders provide an appropriate level of separation of the incoming tightly stacked on-edge signatures from bundles, there are still many instances where the conditions of the incoming signatures exceed the capacity of the automatic loader to operate proper separation. These conditions relate to the properties of the paper web used to produce the signatures, the thickness of the signatures, the type of ink and the density and intensity of the printed indicia. Indeed, when heavy gauge paper with a good absorption rate is bearing light printed text and is folded to form thick signatures, sticking of folded and stacked signatures together is not likely to happen, and automatic loading can be reliably and effectively accomplished with currently available equipment. However, most of the high volume and high speed bindery productions of the present days involve large and thin signatures obtained from light weight glossy paper web printed with colourful heavy indicia. Such conditions are found in the production of magazines, catalogues, and the like and are generally faced on the stitch bindery lines.
In spite of numerous attempts to produce signature bundle loaders providing an appropriate level of separation of the tightly stacked incoming signatures, no currently available equipment can load a stitch bindery line feeding system with a sufficient level of reliability, given the adverse conditions generally encountered during this operation.
Actually, most bundle loaders pay little attention to separation and merely rely on passing the signatures from a first conveyor to a second conveyor sloped upwardly with respect to the first one and driven at a higher speed, thereby making the incoming on-edge signatures to space apart at their upper end and gradually adopt the form of an imbricated or shingled stream. Air jets or physical members are sometimes disposed over the upper edge of the signatures to penetrate between the signatures approaching the second conveyer and force them to separate and urge their forward surface toward the surface of the second conveyor. U.S. Pat. No. 5,374,050 (1994) issued to Prime-Hall Enterprises, U.S. Pat. No. 5,282,613 (1994) granted to R. R. Donnelly and Sons Company and U.S. Pat. No. 4,973,038 (1990) owned by AM International Inc. present examples of that technique which converts stacked onedge signatures to a forward shingle stream, with the side edges of the signatures 1being inclined forwardly and upwardly.
This technique is not much different than the one used in the feeding mechanisms themselves and therefore does not provide a sufficient increase in reliability to hold down times to a reasonable level when used under the adverse conditions generally encountered on stitching lines. For that reason, certain manufacturers such as Harris-Intertype Corp. (U.S. Pat. No. 3,881,718) introduce a transfer of the shingled stream to a third conveyor running at a higher speed than the second one to create an additional relative displacement of the signatures under the shear stress, thus producing a thinner shingle and improving separation. The Harris apparatus also has its third conveyer surface disposed slightly lower than the one of the second conveyor which adds a vertical separating action to the horizontal action provided by the speed change. However, it can be demonstrated that the speed change method as well as vertical stepping become less effective when the signature major faces become substantially horizontal. This is simply due to the fact that the weight of the upstream signatures creates more friction between the layers at such angles, which tends to oppose to the shear stress and keep the signatures attached, while in a more vertical fashion, the weight of the top signatures tends to make them slip downwardly when the lower ones are upwardly accelerated. In a similar manner, a vertical stepping movement will make more effective use of the weight of the signatures for separation when the faces of the signatures adopt a substantially vertical orientation.
Taking into account the fact that on most stitching lines, signatures must be delivered standing on their backbone to form a stack in the hopper of the feeding system, the prior art apparatuses also feature mechanisms to reverse the shingled signature stream or create a shingled stream such that the lagging portion of a downstream signature rests on the surface of the following (upstream) one. This is required when shingled signatures are to be placed substantially vertically in the hopper, since the downstream signatures must not be retained by following signatures in order to fall freely into the hopper. A certain number of mechanisms have been proposed to that effect in the past, and only contribute to add more complexity and risks of malfunction.
Very few examples of apparatuses performing signature separation in a substantially vertical fashion are found in the prior art. A typical approach is to try to replicate the pile bending operation manually carried-out by the attendant. As shown in U.S. Pat. No. 5,244,199 (1993) assigned to St-Denis Manufacturing, U.S. Pat. No. 4,750,728 (1988) granted to Ferag A G and U.S. Pat. No. 4,183,517 (1980) issued to Harris Corporation, the generally upwardly oriented edge standing signatures are passed trough one or more conveyor sections having convergent wall members spaced by an average distance shorter than the width of the signatures. This technique generally requires side conveyors for proper traction of the signatures. This implies more complex mechanisms, additional costs and a wider apparatus while machine spacing is a critical factor to provide enough room for attending and maintenance. Moreover, the number of bending cycles is limited to one or two, with low amplitude and in only one direction, which is a poor substitution for the manually performed operation.
As will be shown in the foregoing description of the present invention, complex mechanisms as described above can be avoided with increased reliability and cost reduction while also avoiding the formation of the signatures into a thin shingle. Furthermore, significant space savings can be achieved by maintaining signatures in a substantially vertical fashion and avoiding transportation over long belt runs in thin shingle form.
The above review of the prior art clearly shows that no reasonably reliable and practical solution to the problem of automatically handling a bundle of signatures to load the feeding system of a stitch binding machine or a comparable piece of equipment has been provided until now.
In accordance with the present invention, there is provided an apparatus for delivering generally flat articles one by one, comprising first and second conveyors. The first conveyor has a top article-supporting surface operated at a first linear speed in a forward direction, wherein, in operation, a stack of generally flat articles lies on one side on the top article-supporting surface longitudinally of the first conveyor. The second second conveyor is installed in series With the first conveyor, operated at a second linear speed higher than the first linear speed in the forward direction, sloping upwardly in the forward direction, and including a plurality of generally parallel, rotative longitudinal screws having respective threads structured to engage a lower edge of the generally flat articles.
The present invention also relates to a method of delivering generally flat articles one by one, comprising:
lying on one side a stack of generally flat articles on a top article-supporting surface of a first conveyor longitudinally of the first conveyor;
driving the top article-supporting surface of the first conveyor at a first linear speed in a forward direction;
transferring the generally flat articles of the stack from the top article-supporting surface of the first conveyor to a second conveyor installed in series with the first conveyor and including a plurality of generally parallel, rotative longitudinal screws having respective threads each defining a succession of ridges and grooves, the transfer of generally flat articles comprising engaging lower edges of the generally flat articles with the threads of the rotative longitudinal screws;
sloping the second conveyor upwardly in the forward direction;
operating the second conveyor at a second linear speed higher than the first linear speed in the forward direction through rotation of the longitudinal screws; and
jogging the generally flat articles by slipping the lower edges of the generally flat articles on the successive ridges and grooves of the threads of the rotative longitudinal screws.
In the above apparatus and method, the jogging movement of the generally flat articles on the successive ridges and grooves of the threads of the rotative longitudinal screws ensure reliable separation of the generally flat articles.
Still according to the present invention, there is provided a method of controlling a conveyor system provided with a discharge end and a top article-supporting surface mobile at a variable linear speed toward a downstream article-processing equipment, wherein, in operation, a stack of generally flat articles is placed on one side on the top article-supporting surface longitudinally of the conveyor system to supply to the equipment generally flat articles one by one from the discharge end. This control method comprises measuring a rate of processing, by the article-processing equipment, of the generally flat articles supplied from the discharge end of the conveyor system, and adjusting the linear speed of the top article-supporting surface in relation to the measured rate of processing.
In accordance with preferred embodiments of the above control method:
the processing rate measurement comprises measuring a speed of rotation of a rotative member of the downstream article-processing equipment; and
the conveyor system further comprises article-detecting proximity sensors mounted at the discharge end, and the linear speed adjustment comprises adjusting the linear speed of the top article-supporting surface also in relation to signals from the article-detecting proximity sensors.
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description of a preferred embodiment thereof, given by way of example only with reference to the accompanying drawings.